Process for producing bisphenol a

ABSTRACT

In the production of bisphenol A by condensation of phenol and acetone with the use of a cation exchange resin as a catalyst and optionally a free mercaptan as a promoter, the degree of conversion of phenol is maintained by increasing the molar ratio of acetone/phenol with the deterioration of the cation exchange resin.  
     With this method, bisphenol A can be effectively produced with industrial advantage.

TECHNICAL FIELD

[0001] The present invention relates to a method of producing bisphenolA [2,2-bis (4-hydroxyphenyl) propane]. More specifically, the presentinvention relates to a method of producing bisphenol A in which, in theproduction of bisphenol A from phenol and acetone with the use of acation exchange resin as a catalyst and optionally a free mercaptan as apromoter, the degree of conversion of phenol is maintained by changingthe reaction conditions with the deterioration of the catalyst, so thatbisphenol A is effectively produced.

BACKGROUND OF THE INVENTION

[0002] Bisphenol A has been known as an important compound for rawmaterial for engineering plastics, such as polycarbonate resins,polyacrylate resins, etc, or for epoxy resins, and the demand for ittends to be still more growing recently.

[0003] Bisphenol A is produced by the condensation of an excess ofphenol and acetone in the presence of an acid catalyst and optionally apromoter, such as a sulfur compound, etc.

[0004] As the acid catalyst for that reaction, inorganic mineral acids,such as sulfuric acid, hydrochloric acid, etc. were conventionally used.However, cation exchange resins have recently attracted attention (GBPatent Nos. 842209, 849565 and 883391), and have come to be industriallyused.

[0005] On the other hand, it has been known that as for sulfur compoundsused as the promoter, alkyl mercaptans with or without substitutinggroups, such as methyl mercaptan, ethyl mercaptan, thioglycolic acid,etc., are useful (U.S. Pat. Nos. 2,359,242 and 2,775,620). Themercaptans function to increase the reaction rate and improve theselectivity. For example, as reaction by-products in the production ofbisphenol A, 2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl) propane (acombination of o- and p′-types) is mainly formed, and tris-phenol,polyphenol, etc. are also formed. Especially, in cases where bisphenol Ais used as raw material for polycarbonate resins, polyacrylate resins,etc., required is colorless high purity bisphenol A containing a reducedamount of those by-products. To this end, mercaptans are used as apromoter in order not only to increase the reaction rate but also tosuppress the formation of the by-products and increase the selectivity.

[0006] With respect to the reaction conditions (the temperature, themolar ration of acetone/phenol) at which phenol and acetone arecondensed to produce bisphenol A, various considerations have been made.For example, Japanese Unexamined Patent Publication No. 54(1979)-19951discloses a method in which the molar ratio between phenol and acarbonyl compound is set to be in the range of 10:1 to 30:1 and thereaction temperature is controlled to be in the range of 40-100° C.;Japanese Unexamined Patent Publication No. 54(1979)-19952 discloses amethod in which the molar ratio between phenol and a carbonyl compoundis set to be in the range of 3:1 to 50:1 and the reaction temperature iscontrolled to be in the range of 30-120° C.; and Japanese PatentPublication No. 63(1988)-52021 discloses a method in which an excess ofphenol is used in an amount of moles four to ten times more than themole(s) of acetone and the reaction is carried out at a temperature inthe range of 40-100° C.

[0007] However, it is the fact that it has not heretofore been practicedto effectively change the reaction conditions with the deterioration ofthe cation exchange resin.

[0008] It has been known that the effect of the reaction temperature onthe improvement in the degree of conversion of phenol is small in thereaction system in which the cation exchange resin is used as a catalystand the mercaptan is used as a promoter. In addition, if one tries todeal with the deterioration of the catalyst through the reactiontemperature, an undesirable situation results: specifically, rapidincrease in the reaction temperature is inevitable. In this case, it isconsidered that elimination of sulfonic groups introduced in generalcation exchange resins is promoted, which may adversely affect thequality of bisphenol A as the product.

[0009] Further, the reason why the degree of conversion of phenol isunlikely to be improved even if the reaction temperature is increased isdeemed to be that in that system the diffusion of the raw material orthe product within the gel structure of the cation exchange resin is therate-determining factor of the reaction rate.

DISCLOSURE OF THE INVENTION

[0010] An object of the present invention is to provide an industriallyuseful method of producing bisphenol A in which, in the production ofbisphenol A from phenol and acetone with the use of a cation exchangeresin as a catalyst and optionally a mercaptan as a promoter, the degreeof conversion of phenol is maintained by changing the reactionconditions with the deterioration of the catalyst, so that bisphenol Ais effectively produced.

[0011] The inventors of the present invention have found, throughextensive studies to achieve the above-mentioned object, that the degreeof conversion of phenol can be effectively maintained and elimination ofsulfonic groups from the cation exchange resin can be suppressed byincreasing the molar ratio of acetone/phenol by not more than 1/20 atone time with the deterioration of the catalyst, whereby the aboveobject can be achieved. The present invention has been made based on theabove finding.

[0012] Specifically, the present invention provides a method ofproducing bisphenol A in which, in the production of bisphenol A bycondensation of phenol and acetone with the use of a cation exchangeresin as a catalyst, the degree of conversion of phenol is maintained byincreasing the molar ratio of acetone/phenol by not more than 1/20 atone time with the deterioration of the catalyst.

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] The method according to the present invention is a method ofproducing bisphenol A in which phenol and acetone are condensed with theuse of a cation exchange resin as a catalyst and optionally a freemercaptan as a promoter. There is no specific limitation with respect tothe kind of the cation exchange resin to be used, and any of those whichare conventionally employed as catalysts for the production of bisphenolA can be used. However, sulfonic acid type cation exchange resins arepreferred especially in terms of the catalytic activity.

[0014] There is no specific limitation with respect to the kind of thesulfonic acid type cation exchange resins to be used inasmuch as theyare strong acidic cation exchange resins having sulfonic groups.Examples of the sulfonic acid type cation exchange resin includesulfonated styrene-divinyl benzene copolymer, sulfonated cross-linkedstyrene polymer, phenol formaldehyde-sulfonic acid resin, benzeneformaldehyde-sulfonic acid resin, etc. These may be used singly or incombination.

[0015] The free mercaptan as the promoter as used herein means acompound having a free form of SH group in the molecule. As the freemercaptan, an alkyl mercaptan can be adopted, which may be either of anon-substituted alkyl mercaptan and a substituted alkyl mercaptan havingat least one substituting group, such as a carboxylic group, an aminogroup, a hydroxyl group, etc. Examples of non-substituted mercaptansinclude methyl mercaptan, ethyl mercaptan, n-butyl mercaptan, n-octylmercaptan, etc. Examples of the substituted alkyl mercaptan includemercaptocarboxylic acids such as thioglycolic acid, β-mercaptopropionicacid, etc., aminoalkane thiols such as 2-amino ethane thiol,2,2-dimethyl thiazolidine, etc., mercaptoalcohols such asmercaptoethanol, etc. Among these, the non-substituted alkyl mercaptansare especially preferred in terms of the cocatalytic action. Inaddition, these mercaptans may be used singly or in combination.

[0016] The amount of each of these mercaptans is generally selected tobe in the range of 0.1-20 mole %, preferably in the range of 1-10 mole%, relative to acetone, which is one of the raw materials to be used.

[0017] Further, there is no specific limitation with respect to theratio of the amount between phenol and acetone, but it is desirable thatthe amount of unreacted acetone is as small as possible in terms of theeasiness of purification of the produced bisphenol A and from aneconomical point of view. Therefore, it is advantageous that phenol isemployed in an amount in excess of its stoichiometric amount. Generally,phenol is employed in an amount of 3-30 moles, preferably 5-15 moles,per one mole of acetone.

[0018] The method of producing bisphenol A according to the presentinvention does not generally require a reaction solvent except for thecases where the reaction is carried out at such low temperatures thatthe viscosity of the reaction liquid is too high or the reaction liquidsolidifies resulting in difficulty in operation.

[0019] The condensation reaction between phenol and acetone in thepresent invention can be carried out in either of a batch-wise mannerand a continuous manner. However, in terms of the production efficiency,preferred is a fixed bed continuous reaction system in which phenol,acetone and optionally above-explained free mercaptan are continuouslyfed to a reaction column packed with a cation exchange resin as an acidcatalyst and are allowed to react. In this respect, the reaction can becarried out with one reaction column, but two or more reaction columnsmay be used so that they are arranged in series. It is industriallyparticularly advantageous to arrange two or more reaction columns eachpacked with the cation exchange resin in series and to use a fixed bedmultiple stage continuous reaction system.

[0020] The reaction conditions for the fixed bed continuous reactionsystem will hereinbelow be explained.

[0021] The molar ratio of acetone/phenol in this reaction is generallyselected to be in the range of 1/30 to 1/3, and preferably in the rangeof 1/15 to 1/5. If this molar ratio is lower than 1/30, there is a riskthat the reaction rate becomes too low. If the molar ratio is greaterthan 1/3, more impurities are generated and the selectivity of bisphenolA tends to be lower.

[0022] Meanwhile, in cases where the free mercaptan is not immobilizedon the cation exchange resin, the molar ratio of the freemercaptan/acetone is generally selected to be in the range of 0.1/100 to20/100, and preferably in the range of 1/100 to 10/100. If this molarratio is lower than 0.1/100, there is a risk that improvements withrespect to the reaction rate and the selectivity of bisphenol A are notsufficiently obtained. If this molar ratio is greater than 20/100,advantages are not fully enjoyed relative to the amount of the freemercaptan used.

[0023] The reaction temperature is generally selected to be in the rangeof 40-150° C., and preferably in the range of 60-110° C. If the reactiontemperature is lower than 40° C., the reaction rate becomes low and theviscosity of the reaction liquid becomes extremely high which may createa risk of solidification. If the reaction temperature exceeds 150° C.,it becomes difficult to control the reaction, the selectivity ofbisphenol A (a combination of p- and p′-types) is lowered, and thecation exchange resin as a catalyst may decompose or deteriorate. Inaddition, LHSV (Liquid Hourly Space Velocity) of the material mixture isgenerally selected to be in the range of 0.2 hr⁻¹ to 30 hr⁻¹, andpreferably in the range of 0.5 hr⁻¹ to 10 hr⁻¹.

[0024] In this kind of condensation reaction between phenol and acetone,the cation exchange resin with which the reaction column is packeddeteriorates with a lapse of a certain time period of operation, andconsequently the degree of conversion of phenol is lowered. In thepresent invention, when the degree of conversion of phenol is lowered tosome extent in that way, the molar ratio of acetone/phenol is firstincreased within the above-mentioned range by once to several hundredtimes, and preferably by once to two hundred times. The degree to whichthe molar ratio of acetone/phenol is increased is set to be such thatthe difference between the molar ratios before and after each increaseat one time is in the range of not more than 1/20. If this degreeexceeds 1/20, a side reaction may occur, so that the yield of bisphenolA may be lowered, and the rate of deterioration of the resin may beincreased. For these reasons, the desirable degree to which the molarratio of acetone/phenol is increased is such that the difference betweenthe molar ratios before and after each increase at one time is in therange of not more than 1/20, and preferably in the range of 1/30 to1/100.

[0025] Meanwhile, if only the reaction temperature is raised withoutincreasing the molar ratio of acetone/phenol, the degree of conversionof phenol may not be improved to a considerable extent, and eliminationof sulfonic groups from the cation exchange resin may be promoted.

[0026] In the method according to the present invention, the reactionmixture coming from the reaction column or columns is subjected to apost treatment in a conventional way, whereby bisphenol A is obtained.

[0027] Explaining an example of the post treatment, concentration isfirst carried out prior to crystallization. Although there is nospecific limitation with respect to the conditions under which theconcentration is carried out, the concentration is generally carried outunder the conditions in which the temperature is in the range of 130° C.to 170° C. and the pressure is in the range of 13 kPa to 53 kPa. If thetemperature is lower than 130° C., high vacuum is requires. If thetemperature is higher than 170° C., more impurities are generated andcolor development is caused thereby. Further, it is advantageous thatthe concentration of bisphenol A in the concentrated residue ranges from25 wt. % to 40 wt. %. If this concentration is less than 25 wt. %, theyield of bisphenol A is low. If this concentration exceed 40 wt. %, itbecomes difficult to carry the slurry after the crystallization.

[0028] Crystallization of an addition product composed of bisphenol Aand phenol from the concentrated residue is carried out by means of thevacuum cooling crystallization method in which cooling is performedusing evaporation latent heat of water generally under reduced pressure.In the vacuum cooling crystallization method, water is added to theconcentrated residue in an amount of 3-20 wt. %, and the crystallizationtreatment is carried out generally at a temperature of 40-70° C. and apressure of 3-13 kPa. If the amount of water added is less than 3 wt. %,heat removing capability is insufficient, and if this amount exceeds 20wt. %, dissolution loss of bisphenol A becomes large, both of whichcases are not desirable. Further, if the temperature of thecrystallization treatment is lower than 40° C., there is a risk ofincrease in the viscosity after the crystallization and occurrence ofsolidification. If the temperature of the crystallization treatmentexceeds 70° C., dissolution loss of bisphenol A becomes larger. Both ofthese cases are not desirable.

[0029] Thereafter, the addition product composed of bisphenol A andphenol as thus obtained by way of the crystallization treatment isseparated by a conventional method, and is then subjected to a washingtreatment generally using phenol. After that, the washed additionproduct is subjected to a disassembly processing into bisphenol A andphenol. The temperature at which the disassembly processing is carriedout is generally selected to be in the range of 130-200° C., andpreferably in the range of 150-180° C. The pressure at which thedisassembly processing is carried out is generally selected to be in therange of 3-20 kPa.

[0030] High quality bisphenol A can be obtained from the bisphenol Athus obtained from the disassembly processing through removing theresidual phenol in the latter bisphenol A substantially completely bythe steam striping method, etc.

EXAMPLES

[0031] The present invention will hereinbelow be described in furtherdetail based on examples. However, the present invention is not limitedto such examples in any way.

Example 1

[0032] Three cylindrical vessels each having an inner diameter of 10 mmand a length of 1500 mm were each packed with a cation exchange resin(sulfonated styrene-divinyl benzene copolymer available from MitsubishiChemical Corporation; Product Name: DIAION SK 104) in an amount of 140milliliters. Then, phenol at a flow rate of 300 g/hr, acetone at a flowrate of 9.3 g/hr and ethyl mercaptan at a flow rate of 0.5 g/hr werecontinuously fed to this set of reaction columns, and were allowed toreact at 75° C.

[0033] In this case, the molar ratio of acetone/phenol was 1/20.

[0034] After a lapse of 100 hours, the degree of conversion of phenolwas 7.2% at that time, and the average degree of conversion of phenolduring that period was 7.5%.

[0035] Then, the reaction was continued in such a manner that the ratesof feeding phenol and acetone were changed so that the molar ratio ofacetone/phenol was set to be 1/15 while LHSV was maintained to be 3hr⁻¹.

[0036] After a lapse of 100 hours from the change in the reactionconditions, the degree of conversion of phenol was 10.0% at that time,and the average degree of conversion of phenol during that period was10.5%.

Comparative Example 1

[0037] Phenol at a flow rate of 300 g/hr, acetone at a flow rate of 18.5g/hr and ethyl mercaptan at a flow rate of 1.3 g/hr were continuouslyfed to the same set of reaction columns as in Example 1, and wereallowed to react at 75° C.

[0038] In this case, the molar ratio of acetone/phenol was 1/10, andLHSV was 3 hr⁻¹.

[0039] After a lapse of 400 hours, the degree of conversion of phenolwas 11% at that time, and the average degree of conversion of phenolduring that period was 12%.

[0040] Then, the reaction was continued in such a manner that the ratesof feeding phenol and acetone were changed so that the molar ratio ofacetone/phenol was set to be 1/5 while LHSV was maintained to be 3 hr⁻¹.

[0041] After a lapse of 50 hours from the change in the reactionconditions, the degree of conversion of phenol was 8.2% at that time,and the average degree of conversion of phenol during that period was9.5%.

INDUSTRIAL APPLICABILITY

[0042] According to the present invention, in the production ofbisphenol A from phenol and acetone with the use of a cation exchangeresin as a catalyst and optionally a free mercaptan as a promoter, thedegree of conversion of phenol is maintained by changing the reactionconditions with the deterioration of the catalyst, so that bisphenol Acan be effectively produced.

1. A method of producing bisphenol A in which, in the production ofbisphenol A by condensation of phenol and acetone with the use of acation exchange resin as a catalyst, the degree of conversion of phenolis maintained by increasing the molar ratio of acetone/phenol by 1/20 orless at one time with the deterioration of the cation exchange resin. 2.A method of producing bisphenol A according to claim 1, wherein thecation exchange resin is a sulfonic acid type cation exchange resin. 3.A method of producing bisphenol A according to claim 1, wherein a freemercaptan is used as a promoter, along with the use of the cationexchange resin as a catalyst.
 4. A method of producing bisphenol Aaccording to claim 3, wherein the free mercaptan is an alkyl mercaptan,mercaptocarboxylic acid, aminoalkane thiol or mercaptoalcohol.
 5. Amethod of producing bisphenol A according to claim 1, wherein the molarratio of acetone/phenol is in the range of 1/30-1/3.
 6. A method ofproducing bisphenol A according to claim 3, wherein the molar ratio ofthe free mercaptan/acetone is in the range of 0.1/100-20/100.
 7. Amethod of producing bisphenol A according to claim 1, wherein thecondensation reaction is carried out at a temperature in the range of40-150° C.